Method for forming serrated or corrugated hollow tubes



H. A. GREIS ETAL 3,407,638

I METHOD on FORMING SERRATED 0R CORRUGATED HOLLOW TUBES Filed March 24. 1966 2 Sheets-Sheet 1 INVENTORS HOWARD A. GREIS VINCENT T. KUBERT, GEORGE H. PETTEE, BY 6. @224,

THEIR ATTORNEY.

Oct. 29, 1968 H. A. GREIS ETAL 7,

METHOD FOR FORMING SERRATED OR CORRUGATED HOLLOW TUBES I Filed March 24, 1966 2 Sheets-Sheet 2 INVENTORS HOWARD A. GREIS, VINCENT T. KUBERT, GEORGE H. P ETTEE,

BY 4/. f. @0734.

THEIR ATTORNEY.

United States Patent 3,407,638 METHOD FOR FORMING SERRATED OR CORRUGATED HOLLOW TUBES Howard A. Greis, Holden, Vincent T. Kubert, Oxford, and

This invention relates to an improved method for producing serrated or corrugated hollow tubes which have particular utility as heat transfer media, as well as other uses.

A distillation apparatus employing serrated or corrugated tubes as heat transfer surfaces has previously been disclosed in U.S. application Ser. No. 242,184, filed Dec. 4, 1962, now Patent No. 3,244,601. These tubes are thinwalled hollow cylinders, having nominal diameters of from 2 /2 to 6 inches, and of varying lengths. The corrugations or serrations are substantially longitudinal and provide both internal and external tube surfaces having alternate ridges and grooves running along the main body of the tube.

Uncorrugated thin-walled tubes of various materials and sizes are readily and economically available; however, the cost of accurately formed serrated or corrugated tubes has been high due to lack of a suitable method for making them economically.

It has been suggested previously, that corrugated or serrated surfaces can be produced either internally or externally upon cylindrical members by modifying conventional thread rolling apparatus. A familiar example of this is found in knurled surfaces. However, difiiculties arise when attempting to provide both internal and external corrugations or serrations on a thin-walled member, so that the transverse thickness of the corrugated wall in the completed member is substantially uniform,

Accordingly, one object of the present invention is to provide an improved method for economically producing thin-walled hollow tubes having regularly spaced, substantially longitudinal corrugations or serrations out of smooth tubes.

Another object of the invention is to provide an improved method for rolling internal and external, substantially longitudinal corrugations in a smooth tube member so that the final product has walls of substantially uniform thickness.

Briefly stated, the invention is practiced by placing a smooth thin-walled hollow tube over a mandrel having longitudinal teeth with uniform spacing. Two or more external toothed dies with a slightly greater tooth spacing are rotated while they are forced radially against the tube, so that the tube wall is deformed between the teeth of mandrel and dies. The tube and mandrel are moved longitudinally between the dies. The mandrel anddies are rotated in synchronism as the process commences, and thereafter only the dies are rotated while radial force is maintained, the deformed tube itself then performingthe synchronizing function.

The invention will be better understood from the following description, taken in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a portion of a corrugated tube fabricated in accordance with the invention,

FIG. 2 is a cross-sectional view of a smooth tube mounted on a mandrel,

FIG. 3 is a schematic plan view of one type of apparatus utilized to mount the uncorru gated tube on the mandrel, I

FIG. 4 is a schematic plan view of the apparatus used to corrugate the tubes,

3,407,638 Patented Oct. 29, 1968 ice FIG. 5 is a cross-sectional view of the tube, mandrel, and dies, taken along lines V, V of FIG. 4,

FIG. 6 is a view, partly in section, illustrating the principle of operation, and,

FIGS. 7 and 8 are sectional longitudinal and transverse views respectively illustrating an alternate means for synchronizing dies and mandrels.

Referring to FIG. 1 of the drawing, a tube 1 has external corrugations or serrations 2 and corresponding internal corrugations or serrations 3. The tube diameter and length will vary according to the type of apparatus in Which it is to be used. The configuration and spacing of the corrugations may also vary as is disclosed, for example, in United States patent application entitled Distillation Apparatus, filed Mar. 1, 1962 and having Ser. No. 176,711, now abandoned. The method herein disclosed can produce configurations ranging from smoothly contoured corrugations to almost V-shaped serrations, all 'of which will be referred to hereinafter as corrugations for convenience. However, it is noted that the external and internal corrugations mate with one another so that the wall thickness of tube 1 is uniform.

Suitable materials for tube 1 consist of various ductile or semi-ductile materials such as copper, -10 coppernickel, aluminum or other readily deformable materials.

Referring to FIG. 2 of the drawing, the first step of the process comprises placing a mandrel having an outside diameter slightly smaller than the inside diameter of the tube 1, within the tube. Mandrel 4 is formed with parallel regularly spaced teeth of the configuration desired. High carbon steel has been found to be a satisfactory material for mandrel 4. The mandrel extends at least the length of tube 1 and fits within the tube.

Referring to FIG. 3 of the drawing, a suitable apparatus for placing tube 1 on mandrel 4 is illustrated. The mandrel includes, on one end, a synchronizing pinion 5 and a connecting shaft portion 6. The end having the synchronizing pinion 5 is abutted against a fixed support 7 while the opposite end is started into one end of tube 1. In the opposite end of tube 1 is placed a cylindrical extension 8 of a movable base 9. Rollers or the like (not shown) may be provided at intervals along the length of mandrel 4 and tube 1 to maintain alignment. Cables 10 and 11, secured to movable base 9, are also connected to the drums of a winch 12. Operation of winch 12 will consequently force tube 1 onto mandrel 4. The end of tube 1 is pulled onto the mandrel until it overlaps the clamping grooves 13 cut in the mandrel.

It should be noted that the diameter of the synchronizing pinion 5 is preferably smaller than the mandrel diameter. This allows the tube to be placed over the mandrel from the other end, as well, which may be preferable if automatic apparatus is to be used.

Referring now to FIG. 4 of the drawing, a suitable apparatus is shown for providing the corrugations or serrations on tube 1. A pair of yokes 1 4 and 15 are adapted for rotatably supporting toothed dies 16, 17 respectively. Yokes 14, 15 are adapted to be skewed in vertical planes, as shown, and means are provided such as hydraulic cylinders (not shown) to force the yokes and dies toward one another, as indicated by the arrows 18, 19, with force sufficient to deform tube 1. A suitable machine for giving the proper pressure and orientation of the dies may be provided by adapting a standard thread rolling machine, such as the Kine-Roller machine, model MC-S-FT, manufactured by Kinefac Corporation of Worcester, Massachusetts. This machine is modified by substitution of the dies 16, 17 for the rollers normally used in thread rolling.

Means for rotating dies 16, 17 at the same speed include a drive motor 20, meshed gears 21, 22 and 23 with universal drive shafts 24, 25 connected to the shafts of dies 16, 17 as will be apparent from the drawing.

A mechanism is provided to clamp tube 1 to mandrel 4, whichis illustrated schematically by a number of wedges 26 driven into clamping grooves 13 (also see'FIG. 3). It will be apparent that there are various types of automatic clamping devices which would also be suitable.

At the other end of tube 1, a movable base'27 (with bearings 28 to allow rotation) serves to exert nominal longitudinal force upon the tube if needed, although in most cases, the skew angle of dies 16, 17 will provide suflicient axial thrust component to move the tube and mandrel longitudinally between the dies as the process takes place.

In order for the tube to have uniform wall thickness, the mandrel and die teeth must rotate in proper phase relationship. This relationship is provided automatically once a section of the tube has been corrugated due to the presence of the deformed tube wall in intimate contact with the teeth of both dies and mandrel. However, at the start of the process, there is no assurance that the teeth of the mandrel and dies will be in registry with one another, i.e., that the crowns of the die teeth will fall exactly between the crowns of the mandrel teeth (similar to meshing gears) so that the wall thickness of the deformed tube will be uniform throughout.

In order to accomplish synchronizing, a synchronizing device shown generally as 29 includes a pair of synchro nizing gears 30, 31 mounted on movable yokes 32, 33 which mesh with the synchronizing pinion 5. Gear 30 is driven from the shaft of die 16 through a universal drive shaft 34 connected thereto by an adjustable coupling 35. It is important to note that universal drive shaft 34 (as well as univensal drive shafts 24,- 25 mentioned previ ously) are of the so-called constant velocity type which provide correspondence of angular velocity between driving and driven shafts. Also, ratio of teeth of the synchronizing gears 30, 31 to synchronizing pinion must be the same as the ratio of teeth of dies 16, 17 to those on mandrel 4. It will be apparent, therefore, that there is a torsion path set up through dies 16, 17, coupling 35, universal drive shaft 34, synchronizing gears 30, 33, synchronizing pinion 5, shaft 6 and mandrel 4, so that when synchronizing gears 30, 31 are in place, mandrel 4 will be constrained to rotate with dies 16, 17.

The coupling 35 is used to adjust for lost motion and torsional elasticity of the path between dies 16, 17 and mandrel 4 so that the dies and the mandrel are synchronized in proper phase relationship when the system is rotating under torsional stress.

The purpose of the movable yokes 32, 33 is to allow gears 31, 32 to pivot away from the synchronizing pinion 5, so that the tube 1 and mandrel 4 will freely pass therebetween, once the synchronizing function has been taken over by the deformed tube wall and the synchronizing gears are no longer needed.

The schematic view of FIGURE 5 illustrates the direction of rotation of dies, mandrel and tube. There it is seen that proper phase relationship of dies and mandrel is provided by the deformed tube, once synchronization is achieved.

Reference to FIG. 6 of the drawing shows the principles governing selection of tooth and skew angles on the dies and mandrel. The, angle of skew A is greatly exaggerated for purposes of illustration only, and would normally be in the neighborhood of /a of a degree to 5 degrees. It will be observed that the teeth 16a on die 16 are helical, so that, at the point of meshing with the deformed tube wall, they lie parallel to the mandrel teeth. Thus if longitudinal tube corrugations are to be formed, the helix angle of die teeth 16a is the same as the angle of skew A. It will also be observed that rotation of die 16 in the direction of arrow 36 causes an axial thrust component on tube and mandrel in the direction of arrow 37, as determined by skew angle A. It is not necessary that the corrugations be 15. Once a short length of tube 1 has been furnished with;

corrugations, as indicated at 38 in FIG. 4, yokes132, 33 are pivoted to disable the synchronizing device and to allow the tubeand mandrel to pass freelybetweenthe synchronizing gears as the process proceeds. Only the" dies 16 and 17 are now being rotated by the motor, while maintaining radial force. Nominal'axial pressure may be" exerted by movable base 27, if desired, to assist in moving the tube and mandrel.

FIGURES 7 and 8 illustrate an alternate'method of synchronizing through the use of a leader member 39 in lieu of the synchronizing device 29 of FIG. 4. In FIGS. 7 and 8, a die 16, mandrel 4 are shown commenced in proper phase relationship by leader 39, which is a piece the shape of a corrugated tube. This is placed on mandrel 4 ahead of the end of tube 1 and it will heapparent that the die and mandrel will be in proper phase relation as the end of tube 1 passes under the starting relief portion 16b of the die. This is a simpler way of achieving synchronization, but it will be seen that it requires more time, is less adaptable to automatic processing, and does not permit forming in middle of tube while leaving ends smooth'for easy mounting and sealing in a heat exchanger. As the tube and mandrel move longitudinally, the leader 39 is disengaged automatically as it moves beyond the die.

After the tube 1 is corrugated to the extent desired, it isremoved from mandrel 4. Although the entire length of tube 1 can be corrugated by the process, it maybe suitable to leave each end smooth, as shown, so that it can be more easily attached to other structural members.

By reference to FIG. 5, it will be apparent-that the circular pitch 'of the die teeth must be the same a's the circular pitch of the teeth of the deformed tube to achieve proper meshing. In other words, the actual cir-, cular pitch of the mandrel teeth must be slightly less than that of the die teeth, due to the fact that the wall thickness of the tube increases the effective circular pitch ofthe mandrel teeth. It will be understood thatth'is inherent relationship applies when the terms equivalent spacing or the like are employed in the claims. l

The process disclosed herein has the advantage of being simple and, moreover, is economical and adapted to use for various diameter tubes by providing different diameter mandrels. Great flexibility is achieved through the factthat the length can be controlled very easily.

While aparticular embodiment of the invention has been illustrated and described, changes and modifications in the process will become apparent to those skilled in the art. It is ,desired to cover inthe appended claims all such-changes and, modifications which do not depart from the true spirit and scope. of the invention. A

What is claimed as new and; desired to be secured by Letters Patent of the United-States is: 1 I,

1. The process' of forming uniform corrugations in a hollow tube comprising:

placing a mandrel having teeth thereon within a. tube, providing a plurality of toothed dies, the die teeth having a spacing equivalent to those on the mandrel, rotating said dies and mandrel together in phase relationship so that the die teeth register with the spaces between mandrel teeth, and

forcing said dies radially against the tube with sufiicient force to cause the tube to deform between die teeth and mandrel teeth, and

rotating the dies alone while maintaining said radial force.

2. The process of forming substantially longitudinal corrugations in a hollow tube comprising:

placing a mandrel having regularly spaced, substantially longitudinal teeth within a tube,

providing a plurality of toothed dies, the die teeth having a spacing equivalent to those on the mandrel, rotating the dies and mandrel in synchronism, so that the die teeth fall midway between the mandrel teeth,

forcing the dies toward the tube to apply radially directed pressure sufficient to deform the tube between die teeth and mandrel teeth,

causing the tube and mandrel to move longitudinally between said dies, and

rotating the dies and mandrel in synchronism, so

the synchronizing function.

3. The process of forming substantially longitudinal corrugations in a hollow tube comprising:

placing a mandrel having regularly spaced substantially longitudinal teeth within a thin-walled tube,

providing a plurality of dies having helical teeth of a slightly greater circular pitch than that of the mandrel teeth as required by the tube wall thickness, and skewed slightly with respect to the tube axis approximately by the amount of the helix angle of said teeth,

rotating the dies and mandrel together in synchronism so that the die teeth fall midway between the mandrel teeth,

forcing the dies radially against the tube with sufficient force to deform the tube wall between die teeth and mandrel teeth, and

rotating the dies alone while maintaining said radial force, allowing the tube and mandrel to move longitudinally between the skewed dies as the deformed tube assumes the synchronizing function.

4. The process of forming substantially longitudinal corrugations in a hollow tube comprising:

placing a mandrel having regularly spaced, substantially longitudinal teeth within a tube,

providing a plurality of toothed dies, the die teeth having a spacing equivalent to those on the mandrel,

rotating the dies and mandrel in synchronism, so that the die teeth fall midway between the mandrel teeth,

forcing the dies toward the tube to apply radially directed pressure sufiicient to deform the tube between die teeth and mandrel teeth, and

causing the tube and mandrel to move longitudinally between said dies.

5. The process of forming substantially longitudinal corrugations in a hollow tube comprising:

placing a mandrel having regularly spaced substantially longitudinal teeth within a thin-walled tube,

providing a plurality of dies having helical teeth of a slightly greater circular pitch than that of the mandrel teeth as required by the tube wall thickness, and skewed slightly with respect to the tube axis approximately by the amount of the helix angle of said teeth,

rotating the dies and mandrel together in synchronism so that the die teeth fall midway between the mandrel teeth,

forcing the dies radially against the tube with suflicient force to deform the tube wall between die teeth and mandrel teeth, and

causing the tube and mandrel to move longitudinally between said dies.

References Cited UNITED STATES PATENTS 214,581 4/1879 Packham 72-105 838,570 12/1906 Numan 72-l05 2,001,553 5/1935 Spencer 72--196 CHARLES W. LANHAM, Primary Examiner.

L. A. LARSON, Assistant Examiner. 

1. THE PROCESS OF FORMING UNIFORM CORRUGATIONS IN A HOLLOW TUBE COMPRISING: PLACING A MANDREL HAVING TEETH THEREON WITHIN A TUBE, PROVIDING A PLURALITY OF TOOTHED DIES, THE DIE TEETH HAVING A SPACING EQUIVALENT TO THOSE ON THE MANDREL, ROTATING SAID DIES AND MANDREL TOGETHER IN PHASE RELATIONSHIP TO THAT THE DIE TEETH REGISTER WITH THE SPACES BETWEEN MANDREL TEETH, AND FORCING SAID DIES RADIALLY AGAINST THE TUBE WITH SUFFICIENT FORCE TO CAUSE THE TUBE TO DEFORM BETWEEN DIE TEETH AND MANDREL TEETH, AND 